1. Field of the Invention
The present invention relates to automatic roll filters and in particular to an improved metering apparatus for regulating the advance of the filter media in such devices.
2. Description of the Prior Art
The prior art discloses a variety of metering arrangements for regulating the advance of roll filter media through the filtering zone of an automatic roll filter. For example, U.S. Pat. No. 3,276,191 shows the use of a weighted drive chain adapted to advance clean filter media into the filtering zone upon displacement of a roller mechanically connected with the chain. In that arrangement, the media is drawn over the roller in a fashion, such when the dust loading in the media reaches a predetermined level, the gas pressure on the media causes the media to displace the roller which in turn releases the chain to advance the media. U.S. Pat. No. 3,310,921 shows another metering arrangement wherein a drive motor is connected to suitable timing and dust load sensing circuitry which includes an electrical shut-off switch actuated by a cam adapted to rotate with the movement of the filter media across the filtering zone. Each time the circuitry activates the drive motor, the cam allows the media to advance a predetermined distance into the filtering zone and then actuates the switch to shut off the motor. While mechanical metering arrangements such as the foregoing have proven satisfactory in many applications, experience has shown that they have been susceptible to misadjustment in the field as well as being subjected to the deleterious effects of wear and corrosion of their various components.